BMI (body mass index) is a measure for body shape and is calculated from the weight and height of an individual for children and adolescents. body mass index is a value derived from the mass (weight) and height of a person The BMI (body mass index) is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m2, resulting from mass in kilograms and height in meters.
BMI (body mass index) may be determined using a table or chart which displays BMI (body mass index) as a function of mass and height using contour lines or colors for different BMI categories, and which may use other units of measurement (converted to metric units for the calculation)
The rule of BMI (body mass index) is a convenient rule of thumb used to broadly categorize a person as underweight, normal weight, overweight, or obese based on tissue mass (muscle, fat, and bone) and height. Commonly accepted BMI (body mass index) ranges are underweight (under 18.5 kg/m2), normal weight (18.5 to 25), overweight (25 to 30), and obese (over 30)
BMI (body mass index) under 20 and over 25 have been associated with higher all-causes mortality, with the risk increasing with distance from the 20–25 range.
BMI(body mass index) is calculated in two steps
BMI(body mass index) = mass (kg)/height (m)2
Example: A 15 years old boy has 45 kg weight and is 5 feet (1.52 meters) tall, his BMI (body mass index) would be:
BMI=45kg/ (1.52m) 2 = 19.48kgm-2
Step 2: percentile ranking
After calculation, the obtained body mass index(19.48kgm-2) is plotted on the BMI-for-age growth charts for either girls or boys to obtain a percentile ranking. The weight can be categorized according to the percentile range:
Less than the 5th percentile
5th percentile to less than the 85th percentile
85th to less than the 95th percentile
Equal to or greater than the 95th percentile
A 15-year-old boy with a BMI(body mass index) of 19.48 would be in the healthy weight category (5th percentile to less than 85th percentile) according to the growth charts.